1. Field of the Invention
Aromatic polyamides are distinguished by high temperature resistance and good mechanical properties. They are used especially for the production of fibers and films (see Elias/Vohwinkel, "New Polymeric Materials for Industrial Use", Series 2, Carl Hanser Verlag 1983, pages 242 ff.).
2. Discussion of the Background
The industrially available products based on aromatic dicarboxylic acids and aromatic diamines do not yet adequately meet the requirements of the trade. Thus, the polyamides based on terephthalic acid and paraphenylenediamine or isophthalic acid and metaphenylenediamine, such as Kevlar.RTM. and Nomex.RTM., for example, do indeed have a high glass transition temperature; however, they can only be melted with decomposition. It is therefore impossible to process these products by injection molding, i.e., they cannot be processed as thermoplastics. Finally, there is a great drawback in the fact that these polyamides are soluble only in sulfuric acid or a few special polar aprotic solvents such as N-methylpyrrolidone, for example, with the addition of inorganic salts such as lithium or calcium chloride.
Processes for the production of aromatic polyamides are known. A good overview can be obtained, for example, from British Patent 1,547,802; J. Poly. Sci., B, 2-4, 369 (1964), and J. Poly. Sci., Poly. Chem. Ed., 24, 701 (1986). These processes basically suffer from the same defects that were mentioned above. Thus, European Patent Application Disclosure No. 0 099 997 does describe the direct preparation in solution, but the reaction times are extraordinarily long, the products are of poor color quality, and the achievable molecular weights are low. On the other hand, the process of German Patent Application Disclosure No. 35 26 622 represents an improvement. However, both processes describe only the preparation of aromatic polyamides that cannot be processed as thermoplastics.
The known amorphous polyamides based on aromatic dicarboxylic acids and aliphatic diamines also do not yet adequately meet the requirements of the trade (for example, see German Patent No. 26 42 244; U.S. Pat. No. 4,369,305; and European Patent No. 0 053 876). It is therefore required to use mixtures of dicarboxylic acids such as terephthalic and isophthalic acid, for example. However, there are still problems even when mixtures are used. In the case of mixtures with a high proportion of isophthalic acid, the glass transition temperature Tg is too low. Conversely, the polyamides with high proportions of terephthalic acid are partially crystalline and no longer transparent. Therefore, it is necessary for their preparation to use specially formulated mixtures of diamines and/or dicarboxylic acids. In occasional cases it is necessary to add lactams or omega-aminocarboxylic acids during the preparation (see U.S. Pat. Nos. 3,150,117; 4,369,305; 3,840,501; 3,842,405; and 4,028,476; German Patent Application Disclosure Nos. 21 56 723; 26 42 244; 29 36 750; and 36 00 015, as well as European Patent Application Disclosure No. 53 876, and Angew. Makromol. Chem. 98, 225 (1981).